Improve content file/folder names handling

Move files/folders renaming functions to core classes.
Query file/folder for renaming by its current path.
Add ability to rename content folders from WebAPI/WebUI.

src/webui/www/private/scripts/file-tree.js

@@ -117,6 +117,7 @@ window.qBittorrent.FileTree = (function() {
 
     const FileNode = new Class({
         name: "",
+        path: "",
         rowId: null,
         size: 0,
         checked: TriState.Unchecked,